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  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
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<body>
  <script>
    // 1. typeof 检测数据类型
    let uname = "张三";
    console.log(typeof uname);
    let age = 20;
    console.log(typeof age);
    let isMarried = false;
    console.log(typeof isMarried);
    let x = null;
    console.log(typeof x);  //object
  </script>
</body>
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